Currently, brass alloy has been used for the materials of civil and industrial water supply systems. The brass alloy generally contains 1.0˜4.0% lead, which can partially dissolve in the water during the process of water supply, the amount of lead release into water will be in excess of the safety standard (for example, under NSF/ANSI Standard 61-2007-Drinking Water System Components, the release amount of lead should not exceed 5 μg/L, and the release amount of antimony should not exceed 0.6 μg/L). For the past few years, however, the medical experts all over the world found that lead has threatened human health and environment sanitation, accordingly, the researches on substitute for lead brass have been developed in domestic and abroad, wherein mainly three alloy systems are adopted: Cu—Zn—Bi system, Cu—Zn—Si system and Cu—Zn—Sb system.
Bismuth is close to lead in the periodic table of elements. It is brittle and has a lower melting-point than lead, and it cannot form solid solution with brass like lead, therefore, currently, bismuth has been studied more frequently and has been used for actual application as lead-free brass alloy, which has become ideal substitute for lead. Tin and nickel are added into most bismuth brass alloys, even expensive selenium is added into a few bismuth brass alloys, making bismuth distribute into the grain and the grain boundary in the form of particulate instead of distributing into the grain boundary in the form of film, which decreases the hot and cold brittleness of bismuth brass. However, since selenium and bismuth have limited resource and higher prices, the costs of the bismuth brass has been retained at high level. In addition, there are problems of worse castability and weldability, narrower forging temperature scare etc., which make the application and development of bismuth brass restricted to some extent.
In recent years, the study and development of lead-free silicon brass has been turned into the high zinc-low copper brass, i.e., change the form, size and distribution of γ phase in the two phase (β+γ) brass by using modification, improve its processing property and performance. However, the cuttability of such lead-free high zincum silicon brass can only achieve to 70%˜80% of HPb59-1.
Chinese patent No. ZL200410015836.5 has disclosed a lead-free free-cutting antimony brass alloy, which is copper-zincum-antimony alloy. Although its cuttability and corrosion resistance have been improved due to the presence of antimony in the alloy, the alloy has not ideal cold processing property, which affects its subsequent processing properties. The relative standard of potable water has strict standards with regard to the amount of Sb, Pb, Cd, As release into water, for example, under NSF/ANSI Standard 61-2007-Drinking Water System Components, the maximum acceptable release amount of Sb is 0.6 μg/L. When the content of Sb are more or equal to 0.2 wt %, the amount of Sb release into water will exceed 0.6 μg/L. This is the most challenge for applying Sb brass alloy into the components such as water tap in the potable water supply system.
Chinese patent No. ZL200710066669.0 has disclosed a high manganese free-cutting copper zinc alloy, and Chinese patent No. ZL 200710066947.2 has disclosed a free-cutting high manganese copper alloy, the manganese is the main alloy element in the above two patents, the differences is the range of manganese content and other alloy elements. As free-cutting high manganese brass alloy, the two alloys have good application prospects. However, the two alloys can not be used as components in the potable water supply system, due to its high Pb content, which results in the excess of Pb maximum acceptable release amount.
At present, lead-free or low lead free-cutting brass, such as high copper silicon brass, high tin-bismuth brass, aluminium brass, antimony brass and so on, can be made into valves using sand casting and punching press methods, when the assembly torque is 90-137 N·m, the concentration of the ammonia water is 14%, and the ammonia fume lasts for 24 hours, only high copper silicon brass and high tin-bismuth brass show good stress corrosion resistance properties. However, such two alloys have high costs, resulting in lacking competitiveness with its products.